In known methods for forming frame corners, the profiles that are to be joined to each other are mitre cut and welded together in the area of the mitre joint. This technique is used both for metal profiles and for plastic profiles.
Welding such profiles in the corner area requires that the profiles that are to be joined each be of identical geometrical configuration in the area of the weld. If this requirement is not fulfilled, and different profile geometries are used, up to now it has been necessary to match the profiles by means of a separating cut that preceeds the welding, in such a way that after this has been done the corner areas can be tightly welded. In many instances, it was not possible to so configure the separating cut as to render a tight weld possible. In this case, one frequently had to dispense with welding and join the profiles at the corners by means of screws.